Good catch and thanks for trying (and confirming the problem). BUT. I haven't used epubcheck so far in my workflow, and I think within reason. What I produce for PG is strictly validated XHTML, which is then compiled into epubs by PG's internal software. Now, carefully inspecting some PG epubs, I find that the "multiple epubcheck errors" boil down to a systematic addition, by PG's epubmaker/ebookmaker of an uncontemplated (according e.g. to
https://www.w3schools.com/tags/tag_a.asp) "tag" attribute inside <link> and <a> html tags. Like
Code:
<a href="@public@vhost@g@gutenberg@html@files@48913@48913-h@48913-h-5.htm.html#nota_25" class="fnanchor pginternal" tag="{http://www.w3.org/1999/xhtml}a">
I doubt that this is the reason for the crash. I found several PG counterexamples with the same attribute (if it is routinely added by the production software on PG thousands of books, then it should not be a problem) which do not seem to crash on my HD. e.g.:
https://www.gutenberg.org/ebooks/44067
https://www.gutenberg.org/ebooks/45037
https://www.gutenberg.org/ebooks/49079
https://www.gutenberg.org/ebooks/44019